This invention relates in general to a universal frequency synthesizer comprising programmable divider circuitry and a phase detector. The universal frequency synthesizer of the present invention is suitable for use in combination with the conventional components of a phase-locked loop frequency synthesizer to produce a plurality of different frequency signals in response to tuning data provided to the universal frequency synthesizer external source.
The conventional phase-locked loop frequency synthesizer structure is basically comprised of a voltage controlled oscillator, a voltage controlled oscillator frequency divider, a phase detector, a reference oscillator, a reference oscillator frequency divider, and a low pass filter. These elements are interconnected to form a closed frequency feedback system. In operation, the voltage controlled oscillator produces an output signal having a frequency related to the voltage signal applied to the control input of this device. This output signal is then provided to a frequency divider whose output is an integral division of the input frequency and is provided to the phase detector where it is compared with a reference signal produced by the output of reference oscillator frequency divider whose input is the reference oscillator. The phase detector is operable to produce an error voltage that is a function of and proportional to the phase and frequency difference between these two signals. The error voltage is then filtered by the low pass filter before being applied to the control input of the voltage control oscillator. The voltage controlled oscillator responds to this filtered error voltage by varying the frequency of its output signal so as to reduce the detected difference in frequency between the compared signals. In this way, the output signal produced by the voltage controlled oscillator has a phase and frequency which is directly related to the phase and frequency of the reference signal.
These prior art phase-locked loop frequency synthesizers have the inherent disadvantage of requiring a physical alteration of the system structure in order to accommodate the wide range of frequency requirements of different frequency synthesizer systems. In order to change the frequency of the signal produced by the voltage controlled oscillator, the frequency of the reference signal or the frequency of the voltage controlled oscillator's output signal must be changed before they are provided to the phase detector. Presently, the frequency of the reference signal may be changed by changing the reference oscillator or by adding a device for dividing the reference signal frequency by a selected fixed value constant before providing it to the phase detector. Similarly, the frequency of the signal produced by the voltage controlled oscillator can be changed by adding a device for dividing it by a selected programmable range before providing it to the phase detector. All of these methods for changing the frequency of the VCO output signal, however, are undesirable because, they require the use of additional circuitry, a change in the physical make-up of the system, and additional design time (and cause increased physical size and increased power consumption) which tends to severely reduce the flexibility of the system and to significantly increase the cost thereof.
It is therefore an object of the present invention to provide a universal frequency synthesizer which provides the major components of a phase-locked loop frequency synthesizer system wherein said universal frequency synthesizer is capable of being programmed to vary the frequency of the output signal produced by the synthesizer's attendant voltage control oscillator without the need for physically altering or adding any elements to the phase-locked loop frequency synthesizer.
A further object of the present invention is to provide a universal frequency synthesizer capable of being incorporated into a phase-locked loop frequency synthesizer wherein said universal frequency synthesizer is constructed of a single design and can be programmed to vary the frequency of the output signal produced by the synthesizer's attendant voltage controlled oscillator.
Another object of the present invention is to provide a universal frequency synthesizer which is capable of providing a frequency prescaler function to the V. C. O.
Another object of the present invention is to provide a universal frequency synthesizer capable of being incorporated into a phase-locked loop frequency synthesizer wherein said universal frequency synthesizer is capable of being programmed to derive a plurality of different reference frequencies from a single reference oscillator.
An additional object of the present invention is to provide a universal frequency synthesizer capable of being incorporated into a phase-locked frequency synthesizer so that the system can be programmed for use in a number of operating environments without the need for changing or adding any physical components to it.
An additional object of the present invention is to provide a universal frequency synthesizer capable of being incorporated into a phase-locked loop frequency synthesizer wherein said universal frequency synthesizer is capable of being manufactured by LSI Techniques making it economical to produce on a mass scale.
Other and further objects of this invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.